1. Field
The present invention relates generally to communications, and more specifically, to deboosting in a communications environment.
2. Background
Wireless communication systems are designed to allow multiple users to share a common communications medium. One such wireless communications system is a code division multiple access (CDMA) system. The CDMA communications system is a modulation and multiple access scheme based on spread-spectrum communications. In a CDMA communications system, a large number of signals share the same frequency spectrum and, as a result, provide an increase in user capacity. This is achieved by transmitting each signal with a different code that modulates a carrier, and thereby, spreads the signal over the entire spectrum. The transmitted signals can be separated in the receiver by a demodulation process using a corresponding code to de-spread the desired signal. The undesired signals, whose codes do not match, contribute only to noise.
The performance of a CDMA communications system may be enhanced by providing powerful coding methods to facilitate forward error correction (FEC) capability. The coding process provides redundancy that the receiver may use to correct errors. This may be achieved by generating a data packet containing systematic symbols and redundancy symbols from a group of payload bits. The systematic symbols replicate the payload bits. A subpacket containing the systematic symbols and a portion of the redundancy symbols may be initially transmitted to the receiver. If the receiver is able to decode the data packet, the remaining redundancy symbols do not need be transmitted to the receiver. If, on the other hand, the receiver is unable to decode the data packet, a new subpacket with different redundancy symbols may be sent to the receiver on a retransmission. The subpackets may be combined and decoded jointly at the receiver, resulting in a very efficient retransmission, because the energy of the previous transmission is not discarded. This process is known in the art as incremental redundancy.
The drawback to incremental redundancy techniques is that the retransmission process consumes valuable resources. Conventional systems employing incremental redundancy have generally been configured to retransmit each subpacket as a stand-alone transmission. That is, the retransmission energy is sufficiently high such that, even if the previous transmissions had not been received, the receiver still has a good chance of being able to decode the retransmission. This is true even when the incremental energy needed to decode the data packet is very small. Accordingly, there is a need for a more efficient and robust methodology for handling retransmissions that takes into account the energy of previous subpacket transmissions derived from the same data packet.